1. Field of the Invention
The present invention relates to a surface emitting laser, a light source, and an optical module.
2. Description of the Related Art
Surface emitting lasers that emit laser light at a wavelength in 850-nm band have been mainly used as light sources for optical interconnection. An integrated circuit (IC) driver normally drives the surface emitting laser of 850-nm band at 3.3 volts, with respect to the energy bandgap of a GaAs-based quantum well of an active layer of the surface emitting laser of this type.
However, not only the surface emitting lasers for optical interconnection, but all the surface emitting lasers are desired to reduce power consumption in the market. To reduce power consumption in such surface emitting lasers, a method of using a surface emitting laser having an oscillation wavelength longer than 850 nm, in which the energy bandgap of the active layer is lowered, and that can further reduce the bias voltage has been studied. By using a strained InGaAs quantum well for the active layer in order to increase the oscillation wavelength, a differential gain is increased and the power consumption can be further reduced.
Conventional surface emitting lasers having a wavelength longer than 850 nm have a structure disclosed in, for example, N. Suzuki, et al., “25-Gbps operation of 1.1-μm-range InGaAs VCSELs for high-speed optical interconnections”, OFA4, OFC2006. The surface emitting laser includes a selectively-oxidized current confinement layer. In the surface emitting laser, distributed Bragg reflector (DBR) mirrors that are multilayer reflection mirrors formed of a periodic structure of a high refractive index layer and a low refractive index layer are used as an optical resonator, and a p-side electrode is formed above the upper DBR mirror.
However, there is a problem that, when a bias current equal to or larger than a threshold current is applied to a surface emitting laser having a conventional structure, power consumption of the surface emitting laser increases.